1. Field of the Invention
This invention relates to the use of sub-critical water extraction to remove polyphenolic compounds from fruits or highly pigmented garden vegetables and their by-products. The process treats whole fruits or vegetables and their by-products or related plant material with water at elevated temperatures and pressures below the critical point of water to extract the polyphenolic compounds for subsequent recovery.
Polyphenolic compounds are a category of phytonutrients known for having significant antioxidant effects. Structurally, these compounds all have an aromatic or phenolic ring and may impart color to fruits and vegetables. Of the numerous classes of polyphenols, the flavonoids are perhaps the most nutritionally important. The flavonoids are secondary plant metabolites that consist of two aromatic rings connected by a three-carbon bridge. The flavonoids include, for example: the isoflavones found in soybeans; tannins (polymers of proanthocyanidins) found in tea and nuts; quercetin found in grapes, lignins found in grains and nuts; and the anthocyanins found in fruits, vegetables and berries.
The anthocyanins are responsible for the bright reds, blues and purples in berries and certain fruits and vegetables. These compounds are active in the visible and UV range, permitting visibility to insects and functioning as sun screen agents to plant tissue. The positive human health effects of anthocyanins have been documented, including improving microcirculation and strengthening blood vessels, fighting viruses, improving night vision and having antioxidant, anti-inflammatory, and anticarcinogenic actions within the body. Thus, there is a substantial market in the United States and other countries for these compounds.
2. Description of the Prior Art
The isolation of polyphenolic mixtures can be expensive, generally requiring a vast quantity of raw materials for the production of a relatively small amount of active compound. Anthocyanin contents in chokeberries are found at levels from 3.1–6.3 mg/g (fresh wt.) with levels varying for different varieties and geographical locations [Plocharski, Fruit Processing, 2(6):85–89 (1992)]. Blueberry varieties have been reported to have highly variable levels of anthocyanins ranging from 0.83–3.7 mg/g (fresh wt.) [Kalt et al., Can. J. Plant Sci., 79:617–623 (1999)]. Ellagic Acid levels in different varieties of strawberries range from 0.43–4.64 mg/g (dry wt.)[Maas et al., Hort. Sci., 26(1):66–68 (1991)]. Other components such as procyanidins and flavanols are found in similarly low levels in fruits depending on growing conditions and cultivars [Rommel et al., J. Agric. Food Chem., 41:1237–1241 (1993); Prior et al., J. Agri. Food Chem., 49:1270–1276 (2001)]. Much of the fruit (whole or partial) harvested in the United States is used for juice processing. However, juices are not the only readily-available sources of polyphenolic compounds. These compounds can also be found in the pomace (spent skins, stems and seeds) remaining after the juicing operation.
The isolation of polyphenolic compounds for the nutraceutical market has been limited to the use of extraction solvents approved for food-grade use such as ethanol and acetone in the United States, and ethyl acetate and methylene chloride in Europe. Even though approved for use in the food industry, these solvents are perceived to varying degrees, as being unsafe and environmentally harmful. Moreover, they are also relatively expensive in comparison with the value of the waste stream obtained from juicing operations. Many fruit and juice processors discard the pomace and thus a potentially valuable source of phytochemical compounds.
Recently, subcritical water extraction (SWE) has been presented as an alternative to organic solvents for isolating valuable components from plant material. For example, kava lactones have been successfully removed from kava root utilizing SWE extraction, and have been found to compare favorably to extractions performed with acetone, methylene chloride or methanol [Kubatova et al., J. Chrom. A., 923:187–194 (2001)]. SWE has also been utilized to obtain extracts from rosemary [Basile et al.; J. of Food and Agric. Chem., 46:5202–5209 (1998)], savory and peppermint [Kubatova et al; J. Chrom. A. 923:187–194 (2001)] and marjoram [Jimenez-Carmona, J. Chrom. 855:625 (1999)].